Induction furnaces



Feb. 12, 1957 B. E. MCARTHUR 2,781,437

INDUCTION FURNACES Filed Sept. 10, 1953 2 Sheets-Sheet l &

INVENTOR,

B/w/oe SQM A+ W 2 Sheets-Sheet 2 Feb. 12, 1957 B. E. MCARTHUR INDUCTION FURNACES Filed Sept. 10, 1953 WATER INLET v1 2 1 E FIIIIL DH United States Patent INDUCTION FURNACES Bruce E. McArthur, Youngstown, Ohio, assignor to Magnethermic Corporation, Youngstown, Ohio, a corporation of Ohio Application September 10, 1953, Serial No. 379,389

9 Claims. (Cl. 219--10.49)

My invention relates to induction furnaces and relates more particularly to induction furnaces in which a tubular heating compartment is surrounded by the convolutions of an inductor coil winding unit, whereby metal work-pieces telescoped within the compartment through one end opening thereof may be inductively heated by the effect of alternating electrical currents of low frequency passed through the winding convolutions of said unit.

More particularly the present invention relates to improvements to a furnace of the general type disclosed in the co-pending application for patent of Lackner et 211., Serial No. 205,766 filed January 12, 1951, now Patent Number 2,676,234, and involves the provision of a doublewalled radially thin tube-like metal liner for the inductor coil unit of any such furnace, said liner comprising a pair of concentric and relatively closely radially interspaced and substantially thin metal walls between which a flow of coolant liquid is continuously passed in an improved manner, during inductive heating of any metal workpiece which is disposed within the radially innermost of said walls. The said liner is adapted to be closely fitted radially within the winding convolutions of said coil unit, and its inner metal wall provides the confining wall of the said compartment.

The tube-like liner thus affords a substantially thin and cool tubular separator and thermal shield which is interposed between the work-piece being heated in the compartment and the said coil unit, and the coolant liquid passed between the said walls conveys heat predominantly communicated to the inner wall from the heated workpiece, which otherwise would be communicated to said unit, from the furnace. As a result, the innermost wall of the liner which in other constructions becomes quite hot, is kept at a relatively low temperature which is conducive to a longer useful life thereof.

Heretofore, a tubular layer of insulating materal has been employed to restrict the transfer of heat radially outwardly from a heated work-piece to said inductor winding, the same being disposed in telescoped relationship within the inductor winding, but in the case of lowfrequency furnaces, for which the liner of my invention is especially adapted, while such insulating material should be relatively thick to afford sufficient thermal insulating qualities, it should be relatively thin, to prevent undesirable lowering of the inductive efliciency of the furnace, since such efiiciency can only be had under conditions of substantially close inductive coupling between the work-piece and the inductor winding.

The usual metal liner, which in such furnaces, is disposed within the layer of insulating material and affords the inner and work-piece engageable wall of the heating compartment, becomes quite hot during heating of the metal work-piece, and resultantly said liner requires relatively frequent replacement.

An electrically non-conducting longitudinal extending seam of the said improved double-walled liner hereof is provided to electrically separate the longitudinal edges ice of the liner at the said seam, for the purpose of preventing electrically induced alternating currents from circuitously traversing said liner walls which would cause inductive heating of the liner. The efliciency of the present liner is still further increased by the provision of means whereby the coolant liquid flowing between the Walls is alternately directed in opposite longitudinal directions in different circuitously disposed portions of space between the inner and outer walls, thereof.

An object of my invention, therefore, is to provide an improved water-cooled liner between the inductor coil unit of a low-frequency induction furnace and the workpiece containing compartment of the furnace.

Another object of my invention is to provide for a double-walled water cooled liner disposed within an inductor coil unit of a low-frequency induction furnace, liquid flow directing means, which are adapted to cause the coolant liquid which is forced between the walls to effect substantially equal cooling effect upon all portions of the exposed inner surfaces of said walls.

Another object of my invention is to provide for greater efficiency, in operation of a low-frequency furnace of the above type.

Another object of my invention is to improve the powerfactor of a low-frequency induction furnace.

Another object of my invention is to increase the useful life of the metal wall of the heating compartment of a low-frequency furnace.

Another object of my invention is to provide a watercooled double-walled liner surrounding the heating compartment of a low-frequency induction furnace, which is of small radial extent and, upon the outer wall of which, a relatively thin layer of heat insulating material, and the inductor windings are successively telescoped.

Another object of my invention is to provide improved means applicable to a low-frequency induction furnace adapted to afford close-coupling relation between the inductor coil unit thereof and a metal work-piece telescoped within said unit, and at the same time to provide an inner metal liner for said unit and to prevent undue heating of said liner.

Another object of my invention is to provide an improved inner metallic tube like liner for an inductor coil unit of a low-frequency induction furnace which is maintained at a low temperature by water-cooling thereof, during operative use of the furnace.

Another object of my invention is to provide, for a double-walled liner adapted to achieve any or all of the above objects, reinforcing means disposed between the walls for supporting the same against displacement, while the liner is subjected to the weight of a work-piece carried on a lower portion thereof.

Other objects of my invention and the invention itself will be apparent to those skilled in the art to which this appertains by reference to the description of an embodiment thereof which follows the drawings hereof and by reference to the drawings thereof, in which:

Fig. 1 is a view, partly in longitudinal medial section, and partly in side elevation of an inductor unit of a low frequency induction furnace which incorporates an embodiment of my invention;

Fig. 2 is a planometric pictorial view of an embodiment of the double-walled, liquid cooled liner of my invention, which is incorporated in Fig. 1;

Fig. 3 is a sectional view of the liner of Fig. 1 taken on the line of section 33 of Fig. 1, said line of section being in a plane normal to the axis of the liner as indicated in Fig. 2;

Fig. 4 is a diagrammatic View of the liner of Figs. 2 and 3, to show the preferred course of liquid ilow through the liner, as afforded by the construction shown.

Fig. 5 is a view of a fragment only, of a double-walled 3 water-cooled liner, which is a second embodiment of my invention, the view being on a line of section corresponding to that of Fig. 3.

Referring to the drawings, and first to Figs. 1 to 4 thereof, the liner 1, shown in Figs. 2 and 3, and shown in applied operative position in Fig. 1, within the convolutions 2 of a low-frequency inductor coil, comprises a pair of concentrically relatively telescoped tube-like metal walls, of which the outermost wall 3 is of such tubular form, and is so dimensioned as to fit tightly within the thin heat-insulating tube 25, of the inductor coil unit.

The walls 3 and 4- are maintained in relatively radially interspaced relation by the relatively interposed end rings (:-6a, the end strips 9--9, and by a plurality of longitudinaliy extending strips, of which those of a set 8, and those of a set 7, are fore-shortened and extend in opposite longitudinal directions.

The ring 6 and the ring 6a, respectively surround different of the end portions of the inner Wall 4, and fit snugly within relatively corresponding end portions of the outer wall 3. Each of the strips of the set '7 extend longitudinally of the liner, from that one of its ends which, as shown at 16 is in abutting relation to the inner side edge of the ring 6 toward, but not entirely to, the relatively opposite ring 6a, while each of those strips of the set 3 extend from its end which is in abutting relation to the inner edge of the ring 6a, toward, but not entirely to, the opposite ring 6. Both rings and all strips are of the same thickness which determines the radial extent of the interior space between the walls 3 and 4 of the liner.

All strips 7 and 8 are preferably, as shown, parallel to each other, and are laterally correspondingly interspaced, and strips of the different sets are alternated around the liner between the terminal strips 6 and 6a.

The end strips 9-9 of the double-walled liner 1, provide end walls for the interior space, between the walls 3 and 4, so that except for the inlet and outlet openings for water or other coolant liquid respectively conducted to and from such liner interior space, by the respective pipes 10 and 20, the liner is a substantially thick liquidtight container.

Although the double-walled container 1, and the inner and outer walls 4 and 3 respectively, are here described as tube-like, a seam, which may be open to provide a circumferential gap 19, serves to prevent the induction of circumferentially directed current flow, in the container 1, when the coil unit 2, Fig. 1, is energized by a flow of low-frequency current, such as 50 or 60 cycles per second,

in order to inductively heat to a substantial degree, the metal work-piece (not shown) which is adapted to be telescopably received in the induction furnace heating compartment 30, i. e. within the inner wall 4, of the liner 1. The exterior longitudinal end edges of the walls 3 and 4, and of the split rings 6 and 6a are preferably welded together, as are also the edges of each strip 9, with the thereby adjacent side edges of the walls 3 and 4, which bound the air-gap 19.

The fore-shortening of the strips 7 and 8 permits a continuous zig-zag passage for water under pressure received from an end of the Water conduit 10, secured within the opening 11 of the liner, the water flow extending longitudinally of the space indicated at 12 in Fig. 3.

Such flow supplied through the pipe 10 and opening 11, is directed as shown by the arrows appearing in Figs. 2 and 4, wherein the flow is shown as being deflected by the strip 6 at the opposite end of the double-walled liner, and passed between the end 13 of the longitudinal strip 7 and said strip 6, thence returns in the opposite longitudinal direction between said strip 7 and the next adjacent strip 8 and then around its end, the longitudinal direction of flow being thus reversed at the fore-shortened ends of each longitudinal strip until the flow reaches the 4 passage 18, 3 and 4, whence it is discharged through the outlet pipe 20.

The materials of the liner walls, and the described strips are preferably of metal, and of these, I prefer that the inner wall 4, at least, be of high heat and of wear resistant material which is not magnetizable, such as some of the stainless steels which have the aforesaid desired qualities to a desirable degree.

l contemplate, also, that the said inner liner wall 4, whi h is most exposed to heat from the work-piece, and ad; tienzlly is most exposed to frictional wear, may be made thicker than the outer wall 3 in the event that a sl id-bar, or equivalent means are not employed to supportingly engage the lowermost portion of the workpiece.

in F 5 i show a fragment of a double-walled liner, whereof the inner wall 44) is thickest, and wherein the longitudinally extending liquid deflecting strips such as at '7 and S in Figs. 2, 3 and 4 are replaced by infolds 7t) and 8%"; of the metal of the outer wall 30; such infolds 7% and 80 may be of the same longitudinal extent and be correspondingly positioned as are the strips and 8 of the first above described embodiment. The infolds extend inwardly to snugly engage the arcuate outer wall surface of the inner wall 40. In all other respects, the liner of Fig. 5 may correspond to that of the said first embodiment, and operate in the said way. The liner of either embodiment may have thicker inner walls, or may have both walls of the same thickness, as desired.

in connection with the above description the liner hereof may be traversed by a coolant liquid at least during inductive heating of the work-piece.

At 21, 22, 23 and 24 I show securing tabs through which machine screws, bolts or the like, such as those shown at 22a and 24a, may be passed to secure an end of the liner such as the end having the so-called end-ring 6a, to an end of the inductor unit, which for such a unit as shown in Fig. l is at the left end thereof. Preferably, the tabs are at that end of the unit which is opposite to the end from which the heated billet or other metal work-piece is discharged after being inductively heated in the compartment.

The zig-zag course of coolant liquid, as described, is desirable in order to ensure that all differently longitudinally disposed portions of the liner are exposed to the liquid while at closely corresponding temperatures.

Ordinarily, under most common conditions, it is not necessary to weld or otherwise integrally secure intermediate portions of the length of the different strips 7 and 3 to the inner and outer liner walls 3 and 4, since passage of a small portion of the liquid flow, laterally past "these strips is usually non-objectionable. An important function of the strips 7 and 8, or the equivalent infolds -80 of the outer wall 3, is to support the inner wall 4 against deflection towards the outer Wall 3, when said inner wall is supporting the weight of the billet or other workpiece.

I am aware that other and perhaps numerous departures may be had from the form and disposition of the various above described instrumentalities but within the scope of the present invention.

I claim:

1. A low-frequency induction furnace having a tubular heating compartment within which a metal workpiece may be inductively heated, and comprising an inductor Winding surroundingsaid compartment, a tubelike liner having a pair of respectively inner and outer cylindrically formed relatively concentric, substantially tube-like, non-magnetizable metal walls disposed in substantially close radially interspaced, relation to each other,

. the relatively superimposed adjacent border portions of said walls being interconnected in liquid sealing relation to each other to provide a substantially thin leakproof annular liquid container having a longitudinally extending seam which is transversely electrically non-conductive and whose outer wall is adapted to be closely sur-' rounded by said winding and whose inner wall is adapted to provide the lateral confines of the said heating compartment and inlet and outlet liquid flow conducting openings for the space between the liner walls, said openings being respectively adapted for the reception of a coolant liquid passed through the first said opening under liquid pressure into the space between the liner walls and for the discharge of water from said space, fluid flow-channelling means disposed interiorly of said container being relatively so disposed as to so direct the course of flow of liquid passed into said space through the first of said openings, that said space will be substantially filled with the fluent liquid prior to discharge thereof from the other said opening, and being further characterized by said liner comprising means interconnecting the interiors of said pair of walls being interconnected at portions thereof to provide a zig-zag channel for the flow of liquid passed from said inlet opening to said outlet opening whereby said liquid is alternately directed longitudinally of the liner in opposite longitudinal directions.

2. A low-frequency induction furnace having a tubular heating compartment within which a metal workpiece may be inductively heated, and comprising an inductor winding surrounding said compartment, a tubelike liner having a pair of respectively inner and outer cylindrically formed relatively concentric,. substantially tube-like, non-magnetizable metal walls disposed in substantially close radially interspaced, relation to each other, the relatively superimposed adjacent border portions of said walls being interconnected in liquid sealing relation to each other to provide a substantially thin leakproof annular liquid container having a longitudinally extending seam which is transversely electrically nonconductive and whose outer Wall is adapted to be closely surrounded by said winding and whose inner wall is adapted to provide the lateral confines of the said heating compartment and inlet and outlet liquid flow conducting openings for the space between the liner walls, said openings being respectively adapted for the reception of a coolant liquid passed through the first said opening under liquid pressure into the space between the liner walls and for the discharge of water from said space, fluid flow-channelling means disposed interiorly of said container being relatively so disposed as to so direct the course of flow of liquid passed into said space through the first of said openings, that said space will be substantially filled with the fluent liquid prior to discharge thereof from the other said opening, and being further characterized by said liner being of sheet metal and each of its said walls being rendered annularly discontinuous by the provision of a longitudinally extending and electrically non-conductive gap extending throughout the length of the liner, by the provision of means to close the spaces between said walls at the longitudinal ends of the liner, and at each side of said gap, and said liner being of a radial thickness which is not in excess of the radial extent of said winding.

3. A low-frequency induction furnace having a tubular heating compartment within which a metal workpiece may be inductively heated, and comprising an inductor winding surrounding said compartment, a tubelike liner having a pair of respectively inner and outer cylindrically formed relatively concentric, substantially tube-like, non-magnetizable metal walls disposed in substantially close radially interspaced, relation to each other, the relatively superimposed adjacent border portions of said Walls being interconnected in liquid sealing relation to each other to provide a substantially thin leal proof annular liquid container having a longitudinally extending seam which is transversely electrically non-conductive and whose outer wall is adapted to be closely surrounded by said winding and whose inner wall is adapted to provide the lateral confines of the said heating compartment and inlet and outlet liquid flow conducting openings for the space between the liner walls, said openings being respectively adapted for the reception of a coolant liquid passed through the first said opening under liquid pressure into the space between the liner walls and for the discharge of water from said space, fluid flow-channelling means disposed interiorly of said container being relatively so disposed as to so di rect the course of flow of liquid passed into said space through the first of said openings, that said space will be substantially filled with the fluent liquid prior to discharge thereof from the other said opening, and being further characterized by the provision of a plurality of liquid deflecting means, each thereof extending longitudinally of the liner and being laterally interspaced from the next succeeding of said means, and successive thereof extending from a difierent longitudinal end of the space between the said inner and outer liner walls in the direction of, but short of the opposite end of said space, whereby liquid under pressure communicated to the space between a first pair of said means is alternatively forced in opposite longitudinal directions, a wall of said space between said first pair of said means having a liquid receiving port therethrough, and a wall of the space between the last pair of said means having a liquid discharge port therethrough.

4. A low-frequency induction furnace comprising a horizontally extending tubular heating compartment adapted to receive a metal work-piece telescoped therein through a longitudinal end opening thereof, an inductor winding surrounding said compartment, a double-walled tube-like liner formed of non-magnetizable metal material, the two walls thereof being relatively telescoped and of such relatively different diameters as to provide a space between them, said liner being provided with a longitudinally extending substantially narrow gap to cause it to be annularly discontinuous, and said liner having a fluid receiving opening adjacent to and atone side of said gap and having a fluid discharge opening adjacent to and at the opposite side of said gap, both of said openings being located near the same longitudinal end of the liner, the inner and outer walls of said liner being interconnected at the longitudinal ends of the liner, and also at the two sides of said gap, to cause said liner to conduct liquid under pressure, communicated to its liquid receiving opening, between said walls to said discharge opening in a leak-proof manner, and said liner adapted to be closely telescoped Within said winding and by its innermost wall to define the confines of said compartment, and being further characterized by the provision of liquid deflecting means adapted to cause said liquid to pass from the inlet to the outlet opening, between said walls, in a zig-zag path, comprising a channel comprising successive horizontally extending sections, wherein the liquid is successively directed in opposite longitudinal directions between end portions of the liner.

5. A low-frequency induction furnace comprising a horizontally extending tubular heating compartment adapted to receive a metal work-piece telescoped there-in through a longitudinal end'opening thereof, an inductor winding surrounding said compartment, a double-walled tube-like liner formed of nou-magnetizable metal material, the two walls thereof being relatively telescoped and of such relatively different diameters as to provide a space between them, said liner being provided with a longitudinally extending substantially narrow gap to cause it to be annularly discontinuous, and said liner having a fluid receiving opening adjacent to and atone side of said gap and having a fluid discharge opening adjacent to and at the opposite side of said gap, both of said openings being located near the same longitudinal end of the liner, the inner and outer walls of said liner being interconnected at the longitudinal ends of the liner, and also at the two sides of said gap, to cause said liner to conduct liquid under pres-sure, communicated to "its liquid receiving opening, between said walls to said discharge opening in a leak-proof manner, and said liner adapted to be closely telescoped within said winding and by its innermost wall to define the confines of said compartment, and said furnace being further characterized by the provision of a plurality of longitudinally extending spacer strips successively disposed in successive amiularly interspaced relation between said liner walls, said strips being shorter than the longitudinal extent of the space between said walls, and successive thereof extending from relatively longitudinally opposite ends of the said space toward the other thereof, whereby a zig-zag channel for liquid flow between said walls is provided by said strips.

6. A low-frequency induction furnace comprising a double-walled tube-like liner whose inner wall provides the lateral wall or" a heating compartment, a single layer inductor winding closely surrounding the liner, said compartment being adapted for the reception of metal workpieces for inductive heating thereof in response to energization of said winding by the effect of a low-frequency alternating current directed therethrough, said liner walls being disposed in concentric relation to'each other, and being of such relative sizes and conformation as to afford a space between them, the concentric walls of said liner comprising metallic material and being rendered electrically non-conductive in the annular direction by the provision of a narrow electrical gap which extends longitudinally from end-to-end of the liner, means adapted to introduce a coolant liquid under pressure into one portion of the space between the liner walls, and means adapted to effect discharge of said liquid from another portion of said space, said space portions being relatively so disposed as to ensure passage of liquid throughout all portions of the said space, and said furnace being further characterized by at least one of said liner walls being so formed as to provide rcentrant portions extending inwardly of said space towards the other wall, said portions adapted to afford deflector means for directing the coolant liquid flow in desired directions during its passage through said space.

7. A low-frequency induction furnace having a tubular heating compartment within which a metal work-piece may be inductively heated, and comprising an inductor winding surrounding said compartment, a tube-like liner having a pair of respectively inner and outer cylindrically formed relatively concentric, substantially tube-like, nonmagnetizable metal walls disposed in substantially close radially iuterspaced, relation to each other, the relatively superimposed adjacent border portions of said walls being interconnected in liquid sealing relation to each other to provide a substantially thin leak-proof annular liquid container having a longitudinally extending seam which is transversely electrically non-conductive and whose outer wall is adapt-ed to be closely surrounded by said winding and whose inner wall is adapted to provide the lateral confines of the said heating compartment and inlet and outlet liquid flow conducting openings for the space between the liner walls, said openings being respectively adapted for the reception of a coolant liquid passed through the first said opening under liquid pressure into the space between the liner walls and for the discharge of water from said space, fluid flow-channelling means disposed interiorly of said container being relatively so disposed as to so direct the course of flow of liquid passed into said space through the first of said openings, that said space will be substantially filled with the fluent liquid prior to discharge thereof from the other said open ing, and said furnace being further characterized by at least one of said liner walls being formed to provide inwardly directed corrugations.

8. A low-frequency induction furnace comprising a horizontally extending tubular heating compartment adapted to receive a metal work-piece telescoped therein through a longitudinal end opening thereof, an inductor winding surrounding said compartment, a double-walled tube-like liner formed .of non-magnetizable metal mate rial, the two walls thereof being relatively telescoped and of such relatively different diameters as to provide a space between them, said liner being provided with a longitudinally extending substantially narrow gap to cause it to be annularly discontinuous, and said liner having a fluid receiving opening adjacent to and at one side of said gap and having a fluid discharge opening adjacent to and at the opposite side of said gap, both of said openings being located near the same longitudinal end of the liner, the inner and outer walls of said liner being interconnected at the longitudinal ends of the liner, and also at the two sides of said gap, to cause said liner to conduct liquid under pressure, communicated to its liquid receiving opening, between said walls to said discharge opening in a leak-proof manner, and said liner adapted to be closely telescoped within said winding and by its innermost wall to define the confines of said compartment, and said furnace being further characterized by at least one of said liner walls being formed to provide inwardly directed cor rugations.

9. A low-frequency induction furnace comprising a double-walled tube-like liner whose inner wall provides the lateral wall of a heating compartment, a single layer inductor winding closely surrounding the liner, said compartment being adapted for the reception of metal workpieces for inductive heating thereof in response to energization of said winding by the efiect of a low-frequency alternating current directed therethrough, said liner walls being disposed in concentric relation to each other, and being of such relative sizes and conformation as to afford a space between them, the concentric walls of said liner comprising metallic material and being rendered electrically non-conductive in the annular direction by the provision of a narrow electrical gap which extends longitudinally from end-to-end of the liner, means adapted to introduce a coolant liquid under pressure into one portion of the space between the liner Walls, and means adapted to effect discharge of said liquid from another portion of said space, said space portions being relatively so disposed as to ensure passage of liquid throughout all portions of the said space, and said furnace being further characterized by at least one of said liner walls being formed to provide inwardly directed corrugations.

References Cited in the file of this patent UNITED STATES PATENTS 2,485,843 Pinkney Oct. 25, 1949 2,665,368 Cutlifi Ian. 5, 1954 2,671,124 Bagley Mar. 2, 1954 2,672,550 Vaughan Mar. 16, 1954 2,676,234 Lackner et al Apr. 20, 1954 2,687,464 Crawford Aug. 24, 1954 FOREIGN PATENTS 512,226 Great Britain Aug. 30, 1939 

